Alpha-contaminated
solid radioactive waste is generated in several plants in the front-end and
back-end of the nuclear fuel cycle. Typical plants producing such waste include
MOX fuel fabrication plants, fuel reprocessing plants and waste management
facilities. The main contaminants of concern are uranium, plutonium and the
other actinides. The disposal of such waste needs to be carried out in
accordance with regulatory guidelines which require that alpha-contaminated solid
waste consignments at levels > 4000 Bq/g may not be disposed of in the
near-surface disposal facilities. It is recommended that such waste should be
stored temporarily in storage facilities from where they can be retrieved at a
later date for ultimate disposal. The storage and disposal of
alpha-contaminated waste is occasionally complicated by the co-existence of
high radiation fields from the - sources present in the waste. Typical
examples include 137+134Cs and 60Co on zircaloy hulls.
This requires that the alpha waste carrying high external fields be stored in
shielded vaults. Since the analysis involves for the most part shielding of
large number of sources and their complex geometries, an elaborate point Kernel
method based computer code QAD CG is used. Sources in the drums containing
Alpha Waste are estimated on the basis of maximum contact dose rate on the drum
which is 6960 mGy/h. The gamma emitting nuclide shall be assumed to be
represented by 137Cs to convert the given dose rate in to the activity.
A selection of 1000 mm as the side wall and top slab concrete thickness is
found to be acceptable. The maximum lateral dose rate is 0.131 µGy/h, and maximum top slab dose rate is
0.651 µGy/h.